Remove all references to localedir from metadata.json

It is not used anymore, now that translations are bundled with
the extension. Also, in the zip files it ended up with my home
folder, which is not nice.

extensions/example/metadata.json.in

@@ -3,6 +3,5 @@
  "name": "Hello, World!",
  "description": "An example extension to show how it works. Shows Hello, world when clicking on the top panel.",
  "shell-version": [ "@shell_current@", "3.2" ],
- "localedir": "@LOCALEDIR@",
  "url": "@url@"
 }